This invention relates to antennas. More particularly it relates to antennas formed of two legs for the reception of two specific frequencies by a connected electronic device. More particularly it relates to dual frequency antennas such as L1 and L2 antennas which are formed on planar substrates, having dual frequency reception for Global Positioning Satellite receivers, and having enhanced nilling or anti-jamming characteristics.
In the field of satellite navigation, there are currently two competing systems, the American GPS which operates on one frequency and which dominates the marketplace, and the Russian GLONASS system which operates on a completely different frequency but yields essentially the same navigation and terrestrial positioning information to users. A third system names Galileo in Europe is also being considered for deployment.
The Global Positioning System (GPS)and the Russian equivalent are worldwide radio-navigation systems formed from a constellation of 24 satellites and their ground stations. GPS uses these xe2x80x9cman-made starsxe2x80x9d as reference points to calculate terrestrial positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to better than a centimeter. In a sense it""s like giving every square foot of surface on the Earth a unique address.
With the rise of GPS technology and its benefits, GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. More recently, GPS is finding its way into cars, boats, planes, construction equipment, farm machinery, and even laptop computers.
The inherent problem with GPS is the strength of the signals broadcast by the orbiting satellites tends to be weak when reaching the Earth situated receivers. Consequently, such receivers are constantly subjected to accidental and intentional jamming or nulling of the received signal due to terrestrial interference from a variety of sources. Such interference can render the terrestrial positioning, mapping, and guiding capabilities of GPS receivers totally useless. This is especially true in military applications where intentional jamming of GPS signals by an enemy use high power transmitters in attempts to jam or render GPS technology inaccurate and ineffective.
In most cases intentional and accidental interference with GPS Satellite signals reaches the GPS receivers from a position on the earth adjacent to the receiver itself. Conventional dipole, stacked patch, and other conventional antennas used for GPS reception generally have a radiation gain pattern which resembles a half circle with the ground position of the receivers located substantially in the center of straight diameters side of that half circle. Consequently, interference either intentional or accidental that may be in an area nearby or adjacent to the receivers can jam it and render it inaccurate at best and potentially useless. Therefore it is highly advantageous to provide a high gain dual frequency antenna with a radiation gain pattern that essentially nulls adjacent terrestrial originating signals while rendering maximum gain from the signals in the direction of orbiting satellites. There is an unmet need for such a dual frequency antenna that is small and easily incorporated into small GPS devices, provides sufficient gain to receive sufficient Satellite signals to render the device accurate, and concurrently negates the accidental and intentionally generated interference that is generated terrestrially in adjacent locals to the receivers.
The preferred embodiments of this invention provides a dual band antenna that provides a radiation gain pattern that maximizes signal reception from orbiting satellites. Concurrently, the device forms a null to signal reception arriving from low or determined angles which might be generated intentionally or accidentally in areas on the earth located adjacent to the GPS receivers. The device features a dual element loop and meanderline design having an L1 in a pictured generally loop shape, formed on a top planar surface of a single substrate mutually coupled to a larger L2 loop antenna formed on the bottom surface of the substrate. However, a meanderline shape might also be used to reach the appropriate length for the desired frequency. A single point feed communicates with the L1 or top loop which functions substantially in the 1.575 Ghz frequency domain which is mutually coupled to the L2 or bottom loop that functions in the 1.227 Ghz area of the spectrum. In this fashion both signals are communicated to the device using the antenna through the single point feed. While the current best mode of the device is in the aforementioned frequency range, it is anticipated that any two frequencies might be received by elements of the proper length dimensions and consequently use of the disclosed device of any two frequencies is anticipated.
As formed, the omni directional dual band antenna provides excellent nulling position alignment between the L1 and L2 radiation gain patterns to negate jamming from adjacent signal sources that may be radiating terrestrially adjacent to the device. The device additionally provides a good return loss of xe2x88x9210 dB for both the L1 and L2 elements with improved axial ratio performance for circular polarization. Mutual coupling, or the induction of current in one element from the radiated fields of the second element, provide communication of the signal received by the L2 meanderline loop antenna to the driven L1 antenna through the substrate which positions the two meander line loops in parallel planes and approximately 0.125 inches apart in the current best mode of the device to facilitate this mutual coupling of the two loop elements. The antenna assembly works either with a ground plane formed below the L2 loop and used in combination herewith, or will work without one.
Although this invention speaks to the field of dual band GPS antennas, the unique principles disclosed in this patent will, to those skilled in the art, cover other bands and frequencies, especially those of the L-band portion of the microwave electromagnetic spectrum ranging from 1 to 2 Ghz, especially where anti-jamming is desirous, and it is appreciated that these be covered within the scope of this patent. As such those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing of other devices, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention.
An object of this invention is to provide a single substrate, dual band antenna for GPS signal reception.
Another object of this invention is to provide such a GPS antenna that may be formed by two loop elements formed on opposite sides of a substrate of proper thickness to communicate through mutual coupling of the elements.
An additional object of this invention is the provision of a small and compact dual band antenna which provides limited or no low angle radiation gain coverage thereby preventing terrestrial jamming of Satellite originated signals.
A still further object of this invention is the provision of a small dual band antenna that has a directional radiation gain pattern to enable the user to steer the device away from any angle of terrestrial radiated signals that may interfere with the device.
These together with other objects and advantages which become subsequently apparent reside in the details of the construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.